This invention relates generally to a bi-stable snap over actuator having a piezoelectric trigger for moving the snap actuator past its snap over equilibrium points whereby the actuator can be moved rapidly from one stable position into the other stable position.
Bi-stable snap actuators have been known and used for some time for various purposes. Typically, this type of device includes a relatively thin arcuate shaped member which has an outer rim section and an inner resilient diaphragm section. With the rim section held in a relatively stationary position, the arcuate shaped resilient diaphragm can be moved from a first stable condition to an equilibrium point, herein referred to as the snap over point, wherein the energy stored in the member forces the diaphragm to rapidly snap over into a second stable position. The energy stored in the snap over actuator can be put to use in cycling such devices as valves, switches and the like.
Snap over actuators can take the form of discs, membranes, beams and the like. When in a first stable condition, a sufficient force can be applied to the member so that it buckles or deforms to a critical point and then rapidly snaps over into a second stable position. The snap over process is reversible and the device can be returned to original stable position by applying a force in the opposite direction. Since two stable or equilibrium states are obtainable, and a maximum critical load is required to snap the member in either direction, the member can be used as a switch, detent, actuator or locking device for many types of applications requiring this type of cycling. The term snap actuator will be used herein to refer to a snap over device suitable for use in all of these applications. A snap over actuator of this type for positioning a valve stem is disclosed in U.S. Pat. No. 3,264,884.
Snap over actuators found in the prior art are generally not very compatible with current day control equipment In addition, the mechanical force required to cycle the device between the stable positions are sometimes difficult to apply and can be relatively high. Because these prior art devices rely strictly upon a mechanically applied force for triggering a snap over action, the repeatability of the action may vary, thus limiting the number and types of applications in which the device can be employed.
It is therefore an object of the present invention to improve snap over actuators.
It is a further object of the present invention to improve the response of a snap over actuator.
A still further object of the present invention is to improve the reliability of snap over actuators.
Another object of the present invention is to reduce the amount of force needed to move a snap over actuator over its snap over equilibrium point.
These and other objects of the present invention are attained by a quick acting bi-stable actuator that includes a bi-stable snap over actuator that is arranged to move between two stable positions and at least one piezoelectric actuator that is arranged to act as a trigger with regard to the snap over actuator to hold the snap over actuator in one stable position at slightly below the snap over equilibrium position. A current is applied to the piezoelectric actuator which reacts to move the snap over actuator past the critical snap over equilibrium point whereupon the snap over actuator moves from a first stable position to a second stable position. In one embodiment of the invention piezoelectric actuators are mounted on either side of the snap actuator and are adapted to trigger the snap over actuator in both directions.